The overall goal of the proposed research is to characterize, isolate and purify the protective antigen(s) of Plasmodium falciparum sporozoites, so that these antigens might be used for a malaria vaccine. This research will focus on the following specific aims: I. To obtain monoclonal antibodies against antigenic determinants of P. falciparum sporozoites. The monospecific antibodies will be used to define sporozoite surface antigens and/or internal parasite components. These antibodies will also be tested for functional activity. II. To surface label sporozoites of P. falciparum and to attempt to identify, by immunoprecipitation, the surface antigens of this parasite. Hyperimmune serum samples of a volunteer immunized against P. falciparum sporozoites, hyperimmune mouse sera, as well as a series of Gambian sera with high antisporozoite antibody titers will be used for immunoprecipitation of a labeled sporozoite extract. III. To develop an assay for determining the presence of protective antibodies, i.e. antibodies which abolish the infectivity of P. falciparum sporozoites. This assay will enable us to establish if monoclonal antibodies and hyperimmune Gambian sera to display sporozoite neutralizing, i.e. functional activity. IV. To metabolically label P. falciparum sporozoites. This will provide information on the biosynthesis of the surface antigens and detect possible precursors, as well as internal antigens.